I am new to django (and have no experience in SQL), so maybe there is no standard way of doing this.
So assume I use the band,person,membership example from http://docs.djangoproject.com/en/dev/ref/contrib/admin/#working-with-many-to-many-intermediary-models
What if I want to make sure, there is at max one membership bertween a fixed person and a fixed band. A person can have only one "invite_reason" and "join_date" for the band. Is there some kind of "unique" flag like for onetomany models.
I guess i can write a routine to check and erase any new ones. Where would one such routine live and what is going to call it (cron, django signals (which i don't understand yet))?